Dual fuel diesel engines



2,909,159 Patented oci. 2o, 1959 2,909,159 y DUAL FUEL DIESEL ENGINES Sylvester C. Britton, Bartlesville,.0kla., assignor to Phillips Petroleum Company, a corporation of `Dwelavi'are Application November i26, 1954, SerialNo. 471,346, ,i

' 9 claims. (C1. 12s- 1) This invention relatesto dual fuel diesel engines: In one of its more specific aspects it relates to Va method for operating a duel fuel diesel engine utilizing a pilot charge A comprising fuel oil and gasoline in order to obtain improved combustion and increased power.` In still another of its more specific aspects, it relates to a method for operating a dual fuel diesel engine soV as to obtain increased knock-limited brake horsepower when employing of the dual fuel diesel engine to utilize gas constitutes a definite advantage. Andl even where the price of gas may be high, the price of fuel oil may be relatively higher per unit of heating value. An additional advantage in using gas as a fuel-lies in the fact that service interruptions need not ocur in the event of a reduction or failure of 'gas supply. Thus,the dual fuel engine can operate at one extreme as a conventional diesel engine and at-the other extreme as a compression ignition engine which employs gas as the primary fuel and Vuses fuel oil only as a means for ignition. Forexample, ywhen -used in" oil elds'with portable drill rigs, the same engine can lbe employed in various locations burning. primarily gas, primarily diesel fuel, or various combinations ofthe two may warrant.

as l circumstances injecting a small pilot charge of fuel oil. This type of engine is usually started on straight diesel fuel using a Vdiesel fuel charge substantially larger than the pilot charge. After operation of the engine has been established, the volume of the diesel fuel charge is reduced to the pilot charge at which time the gaseous hydrocarbon fuel-is supplied to the engine. In accordance with the present invention, an improved fuel mixture is provided for luse as a pilot charge in dual fuel diesel engines.

The following are objects of the invention.

Itis an object of this invention to provide an improved method for operating dual fuel diesel engines.

Another object of the invention is to provide an improved method for operating a dual fuel diesel engine so as to obtain improved combustion and increased power.

Still another object of the invention is to provide an improved method for operating a dual fuel diesel engine utilizing a natural gas fuel contaminated with components which increase the knock tendency of the engine.

A further object of the invention is to provide an Yirnproved fuel mixture for use as a pilot charge in dual fuel diesel engines. f

Otherand further objects and advantages of the invention will become apparent to one skilled in the art upon referring to the following disclosure.

Broadly speaking, the present invention resides in a pilot charge comprising fuel oil and gasoline for use in a dual fuel diesel engine and in a method of operating Dual fuel diesel engines have been used extensively in ypetroleum fields where an abundant sourceof gaseous hydrocarbon, particularly natural gas, is available. It has been found, however, that operation with oil eld natural gas is not always satisfactory. In some instances, especially when the natural gas utilized as the gaseous fuel contains substantial quantities of butane, propane or hydrogen sulfide, the knock-limited brake horsepower of the engine is reduced as a result of the occurrence of destructivecombustion in the cylinders of the engine.

Similar poor operation has also resulted when employing refinery gaseous hydrocarbon streams of propane or an admixture of methane and thane contaminatedV with minor quantities of butane, propane, propylene and/or hydrogen sulfide. An investigation of dual fuel diesel engine performance has indicated that the development the power such an engine utilizing this pilot charge. By operating a dual -fuel diesel engine using the pilot charge of this invention, the knock-limited power output of the engine is increased through the improvement in'combustion obtained by reducing the tendency of detonation to occur in the engine. VWhen operating on a gaseous fuel such as natural gas contaminated with propane, propylene or butene, the method of my invention increases the knocklimited brake 'horsepower of the engine and permits the rateofcontinuous power of the engine to be secured when the performance ofthe engine would otherwise be belowrated value. Additionally, the method of this invention not only increases the knock-limited brake horsepower of a dual fuel diesel engine but also permits operation of the engine at rated continuous power on a gaseous hydrocarbon fuel comprising essentially propane. The attainment of a power output higher than the continuous power of the engine when utilizing dry natural gas as a fuel is also possible lwhen operating the engineutilizing the pilot charge of this invention.

vA more complete understanding of the invention may be obtained by reference to the following discussion and the drawing, in which:

Figure l is a graph illustrating the increase in knocklimited brake horsepower resulting from utilizing the pilot charge of this invention; and

Figure 2 is a graph showing the relationship between knock-limited brake horsepower and different pilot charges 'containing various amounts of gasoline.

I have discovered that the combustion process in a dual fuel diesel engine, and concomitantly the knocklimited brake horsepower of the engine, can be greatly m- Aproved by utilizing as the pilot charge asuitable mixture of diesel fuel, e.g., an oil having an initial boiling point of from about 300 F. to about 370 F. and an end boiling point within the range of from about 510?1 F. to about .670? F., and gasoline. While it is preferred to use a leaded gasoline, e.g., one containing between about 1.5 and 4,-0 milliliters of tetraethyl lead per gallon, it is to be understood that an unleaded gasoline can be utilized as well. .It has been found that the additionV of a gasoline todiesel fuel in an amount in the range of about 10 to 30 volume percent of the diesel fuel results in a pilot charge n whih'gives a significant increase in knock-limited'brake horsepower. The increase in knock-limited brake horsepower obtainable by utilizing a pilot charge mixture comprising fuel oil and gasoline is illustrated graphically in Figures l and 2. Reference to Figures l and 2 indicates that when between about and 30 volume percent gasoline is utilized a substantial increase in knock-limited brake horsepower is obtained. It is noted that for volumes greater than about `30 volume percent gasoline the knock-limited brake horsepower decreases rapidly, indicating that the pilot charge does not ignite the gaseous fuel when greater amounts of gasoline are used.

The amount of the pilot charge used in the operation of dual fuel diesel engines is maintained as small as possible commensurate with obtaining the desired ignition of the gaseous fuel charge. The desirability of using a small pilot charge becomes evident when it is considered that when gas is available, use of even a small amount of a pilot charge becomes in comparison expensive. Accordingly, the pilot charge constitutes generally between about 5 and about 25 percent of the total B.t.u. input at full load and remains at this value for all loads. The upper end of the aforementioned range, eg., between about 17 and 25 percent, is applicable to the operation of higher speed engines. More specifically, it has been found that satisfactory operation is obtained when using between about l0 and 15 cu. mm. of pilot charge for each injection of gaseous fuel.

It is also within the contemplation of lthe invention to utilize water injection in conjunction with the operation of dual fuel diesel engines utilizing the pilot charge of this invention. In accordance with this aspect of the invention, water is injected into the intake air stream.

- gas nozzles.

The pilot charge of this invention may be used in any dual fuel diesel engine employing any well known gas as the :fuel such as wet or dry natural gas, renery gas, manufactured gas, propane, and the like. Accordingly, the pilot charge may be used in conjunction with the operation of either 2-stroke cycle or 4-stroke cycle dual fuel diesel engine.

In a 2stroke cycle dual fuel diesel engine, the entire cycle is completed in one revolution of the crank shaft. The pilot charge is sprayed into hot compressed air and gaseous fuel starting the combustion and liberating the energy for the power stroke which follows. In a uniilow scavenged engine, sometime prior to the end of `the power stroke the exhaust valve opens, allowing most of the combustion products to escape into the exhaust manifold. Shortly thereafter the intake ports open, permitting air and gaseous fuel to be forced into the cylinder. Sometime after bottom dead center, the intake ports close, and shortly thereafter the exhaust valve closes. In the case of a loop scavengcd engine, the piston uncovers an opening in the piston cylinder wall near the end of the power stroke, permitting most of the combustion products to escape into the exhaust manifold. Immediately afterward in the stroke, a second port in the cylinder Wall is uncovered Iby the piston, allowing air and gaseous fuel to be forced into the cylinder. The return stroke of the piston is the compression stroke of the cycle, It is also within the scope of the invention to compress air alone on the compression stroke and then simultaneously inject the gaseous fuel and the pilot charge into the engine through one injection valve.

In a 4-stroke cycle dual fuel diesel engine, two revolutions ofthe crank shaft are required for each power stroke. During an intake stroke, air and gaseous fuel are inducted into the cylinder and thereafter compressed during a compression stroke to raise the temperature to one higher than the ignition point of the pilot charge. The pilot charge is injected into the cylinder slightly before the end of the compression stroke, thereby igniting the gaseous fuel which burns during an expansion or power stroke. The resulting combustion products are purged from the cylinder during lan exhaust stroke. In both types of engines, part load is secured by reducing the 4 gas pressure, thereby increasing the air-fuel ratio.v If the air-fuel ratio by weight exceeds about 40 to 1, the ame may be extinguished-in part as evidenced by unburned gas in the exhaust.

A more comprehensive understanding of the invention may be obtained by reference to the following illustrative examples which are not intended, however, to be unduly limitative of `the invention.

EXAMPLE I A General Motors 3-71 dual fuel diesel engine was used in tests to determine the effect of using the pilot charge of this invention when operating the engine on various gaseous hydrocarbons fuels. The engine consisted of the three cylinder, 2-stroke cycle, 16:1 cornpression ratio, GM 3-71 diesel engine modified for dual fuel operation. The dual fuel modications consisted of the replacement of the standard fuel injector with a DF-60 unit injector for introducing the smaller pilot fuel charge, replacement of the air box handhole covers with special gas manifold handhole covers and modification of each cylinder liner -to provide for the attachment of The governor was also redesigned to accommodate gaseous fuel. The gaseous hydrocarbon fuels were metered and introduced to the fuel manifold through hand pressure regulators which by-passed the Aengine Vgas governor to permit overloading of the engine.

Incipient detonation was detected'by the Phillips 66 Electronic Gating Knockmeter and E-l Detonation Pickup.

The following test fuels were utilized in conducting the tests:

(1) Propane-technical grade.

(2) N-Butane-technical grade.

(3) Natural gas-specific gravity-0.66.

(4) Pilot oil-kerosene, 51.4 cetane number and 538 F. end point.

(5) Regular gasoline-80 percent straight run and 20 percent catalytically cracked stock, 82.4 Research octane number and 2.77 ml. TEL per gallon.

(6) Paraffinic type gasoline- 3 percent n-butane, 11 percent iso-pentane, 2O percent technical n-hexane, 22 percent ASTM n-heptane, 44percent HF heavy alkylate fraction (271-416 F. boiling range), 78.7 Research octanenumber and 3.02 ml. TEL per gallon.V

The results of the tests are indicated below in Tables 1, 2 and 3. In all of the tests injection of the pilot charge was started at about 12 before top dead center Table 1 EFFECT vOF REGULAR GASOLINE CONCENTRATION IN PILOT OIL WITH PROPANE AS PRIMARY FUEL Run 1 2 3 4 5 Engine Speed (r.p.m.) 1, 600 1, 600 1, 600 1,600 1, 600 Load (lbs. 1 13 131 124 121 B. G4. 5 70. 9 69. 8 66. 2 64. 5 B.H.P. Increase, percent 9. 9 8. 2 2.6 0 Vol. Gasoline in Pilot Oil (percent) 0 25. 0 20. 0 10. 0 3. 3 Temperatures F.):

Propane Gas. 88 105 120 120 95 Water Out 200 200 200 200 200 Lube Oil Sump 196 200 200 200 201 Wet Bulb 72 72 Dry Bulb. 82 82 Exhaust Cyl.-

1`. 625 700 700 650 620 690 S00 800 730 690 635 710 700 660 635 88 95 99 98 90 98 105 110 112 100 Pressures:

Propane (p.s.i.g.). l2 10. 5 10. 5 10.5 11.0 Lube Oil (p.s..g.) 50 50 5 50 Barometer (in. Hg) 29. 299 Pilot Oil (p.s.i.g.) 47 45 45 44 47 Air Box (in. g). 7. 3 6. 8 6. 6. 7 7. 3 Exhaust (in. Hg) 0. 30 0. 55 0.55 0.55 0.60 Corrected Propane (cfm. 5. 70 5. 82 5. 33

Piiot oil charge 12.7 cu. nzlmJcylinder.` 33.3 %,40.0%, and 50.0% gasoline in pilot oil'would not ignite charge.

Talie 2,.' EFFECT OF PARAFFINIC GASOLINE CONCENTRATION IN PILOT OIL WITH SIMULATED WET' NATURAL GAS A"1 AS PRIMARY FUEL f z- Run. I 1 2 f 3 4 5 Engine Speed (r.p.m.) 1, 600 1, 600 1,600 1,600- 1,2600 Load (lbs.) 126 136 135 133 130 67. 2 72. 5 72. 0 70. 8 69. 3 B.H.P. Increase (percent) 7. 3 7.2 5. 4 3.1 Vol. Gasoline in Pilot Oil (percent) 25.0 20.0 10. 0 5. 0 Temperatures F ater Out- 200 200 200 200 200 Lube Oil Sump. 223 223 221 223 223 Dry Natural Gas.-. 92 96 98 98 98 Propane Gas 150 155 151 152 152 Wet Bulh 71 Dry Bulb 89 Exhaust Cyl.-

1 625 675 670 660 640 2- 700 775 755 750 720 3 625 650 665 655 640 Intake Air 99 99 101 99 100 Pressures:

Natural Gas (p.s.l.g.)-. 13.0 13.0 13.0 13. 0 13.0 Propane (p.s.i.g.) 10.0 10. 0 10.0 10. 0 l0. 0 Lube Oil (s.l.g.)..-.-- 50.0 50.0 50. 0 50.0 50.0 Barc. (in. g) 29. 387 Pilot O11 (p.s.l g 46 46 46 46 46 Air Box (ln Hg 7.1 6. 9 6. 9 7.0 7.0 Exhaust (in. Hg) 0. 55 0.55 0. 55 0. 55 0.55 Bry Corrected Natura Gas (c..m. 2. 84 3. 53 3. 52 3.70 3. 52 Corrected Propane (c.f.m.) 4. 31 4. 62 4. 58 4. 58 4. 37

Pilot oil charge 12.7 cu. mn1.]cy1inder.

33.3% gasoline in pilot oil would not ignite charge.

1 Simulated wet gas A composed of 56.6% C|B| and 43.4% 0.66 sp. gr. dry natural gas.

Table 3 EFFECT OF PARAFFINIC GASOLINE CONCENTRATION IN PILOT OIL WITH SIMULATED WET NATURAL GAS B"l AS PRIMARY FUEL Run 1 2 3 4 Engine Speed (r.p.m.) 1, 600 1,600 1, 600 1, 600 Load (lbs.) 126 130 129 128 B.H.P 67. 2 69. 3 68. 8 68. 3 B.H.P. Increase (percent) 3. 1 2. 4 1. 6 Vol. Gasoline in Pilot Oil (percent) 0 20.0 10.0 5.0 Temperatures F.:

635 660 650 646 710 740 735 725 3 625 645 640 635 Intake Air 92 92 94 95 Prcssures:

Dry Natural Gas (p.s.i.g) 13. 0 13.0 13.0 13.0 N-Butane Gas (p s l g 8. 8. 0 8.0 8.0 Lube O11 (D. 50 50 50 50 Baro. (in g) 29. 329 Pilot Oil 46 45 45 45 Air Box (1n. Hg).---- 7.2 7.1 7.1 7 2 Exhaust 0. 55 0. 55 0.55 0.55 Corrected Dry Natural Gas 9. 67 11. 48 11. 30 10. 25 Corrected N-Butane Gas (c..m.)..-.- 1. 49 1.35 1. 47 1. 34

Pilot oil charge 12.7 cu. mnL/cyllnder.

25.0% gasoline in pilot oil would not ignite charge.

l Simulated wet gas 13" composed ol' 11.7% N-CHio, and 88.3% 0.66 sp. gr. dry natural gas.

(BTDC) and completed at about 3 BTDC. The gaseous fuel was inducted into the cylinder 48 before bottom dead center (BBDC) and continued until about 48 after top dead center (ATDC). Ignition of the gaseous fuel -took place at approximately 15 after top dead center (ATDC).

Results shown in Table 1 indicate that 25 percent gasoline in pilot oil increased the knock-limited brake horsepower with propane by 9.9 percent over straight pilot oil. Concentrations over 33.3 percent would not ignite the primary fuel charge while concentrations less than 25 percent gave less power. Diesel rated continuous power is 67 at 1600 R.P.M.

Table,2 shows theresults whena parainc gasoline of regular quality was blended into 'the pilot oil in various concentrations with a simulated l'natural gas coniposed of 43.4 percent 0.66 specific gravity natural gas and 56.6 percent; propane. Again`25 percentgasoline appeared to be the optimum concentration in the pilot oil. Results show a 7.3 percent increase in lrnocklimited brake horsepower.l @I

Table 3 shows the results when a paraiinic gasoline of regular quality was blended into the pilot oil in various concentrations with a simulated wet natural gas composed of 88.3 percent 0.66 specific gravity natural gas and 11.7 percent normal butane. It was determined that 20 percent parainic gasoline in the pilot oil was the optimum blend.

EXAMPLE II The GM 3-71 diesel engine of Example I was operated on a gaseous fuel of propane with a pilot charge of 12.7 cu. mm./cylinder of 51.4 cetane diesel fuel. The knocklimited brake horsepower developed by the engine at 1600 R.P.M.s was 64.5.

EXAMPLE 111 The GM 3-71 diesel engine of Example I was operated on a gaseous fuel of propane with a pilot charge of 12.7 cu. mm. of a diesel fuel containing lead. A 51.4 cetane diesel fuel containing 1.5 milliliters of tetraethyl lead per gallon of fuel was used. The knock-limited brake horsepower developed by the engine at 1600 R.P.M.s was 65.0. A comparison of the results of Examples II and III indicates that the addition of lead alone to the diesel yfuel pilot charge had no 'appreciable effect on the knock-limited brake horsepower developed by the engine.

As will be evident to those skilled in the art, various modifications of this invention can be made or followed in the light of the foregoing disclosure and discussion withoutdeparting from the spirit or `scope of the invention.

I claim:

1. A method of operating a dual fuel diesel engine which comprises injecting a pilot charge comprising fuel oil and between about 10 and 30 volume percent gasoline, based on the amount of fuel oil, into a combustion zone containing a compressed mixture of a gaseous hydrocarbon and air, thereby igniting said mixture; burning said mixture within said combustion zone; and exhausting the resulting combustion products from said combustion zone.

2. The method of claim 1 in which said gasoline is unleaded gasoline. t

3. The method of claim 1 in which said gasoline contains between 1.5 land 4.0 milliliters of tetraethyl lead per gallon of gasoline.

4. The method of claim 1 in which said gaseous hydrocarbon is dry natural gas.

5. The method of claim 1 in which said gaseous hydrocarbon is wet natural gas.

6. The method of claim 1 in which said gaseous hydrocarbon is propane.

7. A method of operating a dual fuel diesel engine which comprises injecting a gaseous hydrocarbon and air into a combustion zone so as to form a gas-air mixture therein; compressing said mixture in said combustion zone to a temperature at least as high as the ignition temperature of a pilot charge comprising fuel oil and between 10 and 30 volume percent gasoline, based on the amount of fuel oil; injecting said pilot charge into said compressed mixture, thereby igniting same; burning said mixture in said combustion zone, thereby releasing energy; and exhausting the resulting combustion products from said combustion zone.

8. The method of claim 7 in which said gasoline is unleaded gasoline.

. 7 e *i 9. The method of claim 7' in which said gasolie' con- FOREIGNk PATENTS tzns4 between 1;5 V and 4:0 milliliters f -te'eraethylv lead 4434x631 Graf Btan. Sept; 5,193.5 PE1' gallon ofgasolme" e i 7,657 Great Britain Dec. r4, l1.898 .References Cited' in the le of this patent A I OTHER REFERENCES Y Y UNITED STATES PATENTS K Internal C'ombustn Engines-'Lichtyz page 1'32f6tl v673,160 Diesel Apr. so, 1,'901 edition, 19511,; McGraw-muco., New-York. 

